Silicon nitride-containing ceramic material prepared by pyrolysis of hydrosilazane polymers from (R3 Si)2 NH and HSiCl3

ABSTRACT

A process is disclosed for preparing R 3  SiNH-containing hydrosilazane polymer by contacting and reacting trichlorosilane with a disilazane (R 3  Si) 2  NH where R is vinyl, hydrogen, phenyl, or alkyl radicals containing 1 to 3 carbon atoms. These hydrosilazane polymers are useful, when fired at high temperatures, in the formation of silicon nitride and silicon nitride-containing ceramic materials.

This is a divisional of co-pending application Ser. No. 555,755 filed onNov. 28, 1983.

BACKGROUND OF INVENTION

This invention relates to the preparation of hydrosilazane polymers bythe reaction of disilazanes with trichlorosilane, HSiCl₃. Such polymersare useful, when fired at high temperatures, in the formation of siliconnitride and silicon nitride-containing ceramic materials.

What is disclosed herein is a novel process to obtain novelhydrosilazane polymers which consists of contacting HSiCl₃ withdisilazanes in an inert, essentially anhydrous atmosphere whiledistilling volatile by-products.

As is well known in the art, halosilane monomers will react with ammoniaand most organic compounds containing a primary or secondary amino groupto give a variety of silazanes. For example, the reaction oftrimethylchlorosilane and ammonia produces hexamethyldisilazane, asilazane monomer, while dimethyldichlorosilane and ammonia producedimethylcyclic silazanes.

Silazanes in general have been academic curiosities for many years and avariety of such silazanes, including monomers, oligomers, cyclics andeven low molecular weight resins and linear polymers have been preparedby a variety of methods. For example, L. W. Breed et al. in J. Org.Chem., 27, 1114(1962) report the formation of silazanes from thepolymerization of sterically hindered silazane oligomers. In J. Polym.Sci. A, 2, 45(1964), cyclic trimer and tetramer silazanes are reportedto be thermally cracked, using catalysts, to give linear polymers.

In contrast, fluids, rubbery polymers and resins prepared from CH₃SiCl₃, (CH₃)₂ SiCl₂ and excess ammonia have been reported by Kruger etal. in J. Polym. Sci. A, 2, 3179(1964) and by Redl in "SilazanePolymer", ARPA-19, Advanced Research Projects Agency, October, 1965.

The patent literature also contains disclosures of the preparation ofsilazanes. Cheronis in U.S. Pat. No. 2,564,674 (Aug. 21, 1951) disclosesthe preparation of low molecular weight linear silazane polymers by thereaction of halosilanes with excess ammonia in a solvent solution.Bausma et al. in U.S. Pat. No. 3,809,713 (May 7, 1974) discloses asimilar reaction scheme with the added modification of removing theby-produced solid ammonium halide using ethylene diamine.

Verbeek et al. in U.S. Pat. No. 3,853,567 (Dec. 10, 1974) and U.S. Pat.No. 3,892,583 (July 1, 1975) disclosed that mixtures of CH₃ SiCl₃ and(CH₃)₂ SiCl₂ can be treated with ammonia or organoamines to formmaterials that can be pyrolyzed to yield SiC/Si₃ N₄ ceramics.

In another segment of the prior art, the use of disilanes in thepreparation of silazane polymers has been limited to the formation ofrelatively low molecular weight materials. In one example, Wannagat etal., Ang. Chem. 75(7), 345(1963), reported the reaction oftetramethyldichlorodisilane with gaseous ammonia to give a six-memberedcyclic silazane, [(CH₃)₂ SiSi(CH₃)₂ NH]₂, rather than the expectedlinear silazane polymer. Hengge et al., Montash. Chem. 101(2),325(1970), prepared dimethylamino substituted mixtures of disilanes fromdimethylamine and a chlorine-containing disilane mixture obtained fromthe direct process for the preparation of chlorosilanes.

More recently, Gaul in U.S. Pat. Nos. 4,312,970 (Jan. 26, 1982) and4,340,619 (July 20, 1982) has disclosed processes for preparing silazanepolymers by reacting disilazane with either organochlorosilanes orchlorine-containing disilanes. The organochlorosilanes of U.S. Pat. No.4,312,970 are described by the formula R_(n) 'SiCl_(4-n) where R' is avinyl radical, an alkyl radical of 1-3 carbon atoms, or a phenyl radicaland n has a value of 1 or 2. The chlorine-containing disilanes of U.S.Pat. No. 4,340,619 are described by the general formula (Cl_(a) R_(b)'Si)₂ where R' is a vinyl radical, an alkyl radical of 1-3 carbon atoms,or a phenyl radical and where a has a value of 0.5-3, b has a value of0-2.5, and the sum (a+b) is three. Ceramic materials prepared by firingthe preceramic silazane polymers of Gaul at elevated temperatures underan inert atmosphere contained mainly silicon carbide as the crystallinephase. Silicon nitride, if found at all, was present in only minoramounts.

Seyferth et al. in U.S. Pat. No. 4,397,828 (Aug. 9, 1983) disclosed thepreparation of relatively stable, liquid polymers containing silicon,nitrogen, and hydrogen which were formed by reacting dihydrodihalosilanesuch as H₂ SiCl₂ with ammonia in the presence of a solvent comprising analiphatic ether, a chloromethane, or mixtures thereof. The method ofSeyferth et al. produces rather large quantities of the troublesomeby-product ammonium chloride. The liquid polymers were stable, under aninert atmosphere, for at least 7 days at 0° C. but began to gel at roomtemperature after only 2 days. The liquid polymers of Seyferth et al.,upon being fired to elevated temperatures under an inert atmosphere,yielded silicon nitride containing materials.

What has been newly discovered is the coreaction between trichlorosilaneand disilazanes to give useful high molecular weight hydrosilazanepolymers. The hydrosilazane polymers represent a significant advancementover prior art materials.

THE INVENTION

This invention relates to a process of preparing a R₃ SiNH-containinghydrosilazane polymer, which process consists of contacting andreacting, in an inert, essentially anhydrous atmosphere, trichlorosilanewith a disilazane at a temperature in the range of 25° to 300° C. whiledistilling by-produced volatile products, wherein said disilazane hasthe general formula

    (R.sub.3 Si).sub.2 NH

where R is selected from the group consisting of vinyl, hydrogen,phenyl, and alkyl radical containing 1 to 3 carbon atoms.

This invention also relates to a new and novel composition of matterwhich is a R₃ SiNH-containing hydrosilazane polymer which is prepared bycontacting and reacting, in an inert, essentially anhydrous atmosphere,trichlorosilane with a disilazane at a temperature in the range of 25°to 300° C. while distilling by-produced volatile products, wherein saiddisilazane has the general formula

    (R.sub.3 Si).sub.2 NH

where R is selected from the group consisting of vinyl, hydrogen,phenyl, and alkyl radicals containing 1 to 3 carbon atoms.

This invention further relates to a method of preparing a siliconnitride-containing ceramic material which method consists of heating aR₃ SiNH-containing hydrosilazane polymer in an inert atmosphere or in avacuum to a temperature of at least 750° C. until said R₃SiNH-containing hydrosilazane polymer is converted to a siliconnitride-containing ceramic material, said hydrosilazane polymer havingbeen obtained by a process which consist of contacting and reacting, inan inert, essentially anhydrous, atmosphere, trichlorosilane with adisilazane at a temperature in the range of 25° to 300° C. whiledistilling by-produced volatile products, wherein said disilazane hadthe general formula

    (R.sub.3 Si).sub.2 NH

where R is selected from the group consisting of hydrogen, vinyl,hydrogen, phenyl, and alkyl radicals containing 1 to 3 carbon atoms, andphenyl.

The present invention concerns a new class of silazane polymers preparedfrom disilazanes and trichlorosilane. The chlorine-containing silane istreated with a disilazane, as the nitrogen source, in sufficient amountsto react with all of the chlorine in the chlorine-containing silane.This is usually an equimolar amount based on the chlorine content of thetrichlorosilane. The inventor does not wish to be held to such a theorybut it is believed that when the mixture containing trichlorosilane anddisilazane is heated, in an inert essentially anhydrous atmosphere andusually in the absence of solvent, the reaction

    ═Si(H)Cl=R.sub.3 SiNHSiR.sub.3 →=Si(H)NHSiR.sub.3 +R.sub.3 SiCl

takes place. The R₃ SiCl which is produced during the reaction isremoved by distillation as the reaction proceeds. As the temperature ofthe reaction mixture is raised, condensation reaction begins to occur,causing formation of a higher molecular weight hydrosilazane and [R₃Si]₂ NH. The [R₃ Si]₂ NH is also distilled from the reaction as it isformed.

    2=Si(H)NHSiR.sub.3 →=Si(H)NHSi(H)=+[R.sub.3 Si].sub.2 NH

As higher temperatures are reached, more crosslinking occurs and any R₃SiNH-- left in the polymer acts as an endblocker. This method permitsone to stop the reaction at any point to obtain almost any desiredviscosity. The hydrosilazane polymers range in physical appearance fromhigh viscosity liquids to solid materials. The materials are thereforevery easy to handle.

The present invention involves the reaction of trichlorosilane, HSiCl₃,with certain disilazanes to produce hydrosilazane polymers. Thesehydrosilazane polymers may be fired to obtain silicon nitride-containingceramic polymers. It is preferred that the chlorosilane reactant bepurified before it is reacted with the disilazane. It appears that somecomponent, possibly a hydrolysis product, in aged chlorosilane reactantsis detrimental to the process of this invention. Such contaminatedchlorosilane reactants can be suitably purified by distillation. Otherpurification methods may also be employed. It is also preferred that thereactants be added in such a manner that the initial reaction exothermis kept to a minimum. One reactant may be added slowly to the otherreactant, or the added reactant may be cooled, or the reaction vesselmay be cooled to keep the reaction exotherm low. Other methods orcombination of methods may also be used. In general, it is preferredthat the reaction be controlled such that the initial reactiontemperature due to the exotherm is less than about 50° C., and mostpreferably, less than 35° C. In general, more reproducible results areobtained when purified trichlorosilane is used and when the initialreaction exotherm is controlled carefully.

The second reactant in this invention is a disilazane of the generalformula (R₃ Si)₂ NH. R in this formula is vinyl, hydrogen, phenyl oralkyl radical of 1-3 carbon atoms. Therefore, R for purposes of thisformula is represented by hydrogen, methyl, ethyl, propyl, vinyl orphenyl. As set forth above, each R group in this formula can be the sameor they can be different. Examples of compounds contemplated within thescope of this invention include:

[(CH₃)₃ Si]₂ NH, [C₆ H₅ (CH₃)₂ Si]₂ NH,

[(C₆ H₅)₂ CH₃ Si]₂ NH, [CH₂ ═CH(CH₃)₂ Si]₂ NH,

[CH₂ ═CH(CH₃)C₆ H₅ Si]₂ NH,

[CH₂ ═CH(C₆ H₅)₂ Si]₂ NH,

[CH₂ ═CH(C₂ H₅)₂ Si]₂ NH, [H(CH₃)₂ Si]₂ NH and

[(CH₂ ═CH(C₆ H₅)C₂ H₅ Si]₂ NH.

These reactants are brought together in an inert, essentially anhydrousatmosphere. For purposes of this invention what we mean by "inert" isthat the reaction is carried out under a blanket of inert gas, such asargon or nitrogen or helium. What we mean by "essentially anhydrous" isthat the reaction is preferably carried out in an absolutely anhydrousatmosphere but minute amounts of moisture can be tolerated.

When the reactants are contacted with each other, the reaction beginswhich forms an intermediate amino compound. As noted earlier, it ispreferred that the reactants are contacted in such a manner to keep theinitial reaction exotherm to a minimum. Upon heating, additional aminocompound is formed and, upon continued heating, R₃ SiCl is distilledfrom the reaction mixture and a hydrosilazane polymer is formed. Forbest results the rate of heating should be controlled at a rate of lessthan about 1.0° C./min. A heating rate of about 0.5° C./min or less ispreferred. The order of addition of the materials does not appear to becritical. As the temperature is raised more condensation takes place andcrosslinking occurs with residual R₃ Si-- that is not distilled from themixture also acting as a chain-stopper. The desirable temperature rangefor this reaction is 25° C. to 300° C. A preferred temperature range forthis reaction is 125°-275° C. The length of time that the reactionrequires depends on the final temperature of the reaction and the rateof heating. The reaction may be held at the final temperature forvarying lengths of time if desired.

What is meant by "volatile products" are the distillable by-producedproducts that are formed by the reactions set forth above. Thesematerials can be represented by (CH₃)₃ SiCl, (CH₂ ═CH)(C₆ ₅)₂ SiCl, CH₃(C₆ H₅)₂ SiCl, (CH₃)₂ C₆ H₅ SiCl and (CH₂ ═CH)(CH₃)₂ SiCl. Sometimes,these materials require the use of a vacuum along with heat in order toremove them from the reaction mixture.

The hydrosilazane polymers are essentially ready to use. It ispreferred, however, that the hydrosilazane polymers be vacuum strippedprior to use in order to remove volatile materials. Using the vacuumstrip procedure usually results in a solid hydrosilazane polymer whichis easy to handle in further processing steps. The hydrosilazanepolymers are pyrolyzed in an inert atmosphere or in a vacuum attemperatures of at least 750° C. to give silicon nitride-containingmaterial. If the polymer is of sufficient viscosity or if it possesses asufficiently low melt temperature, it can be shaped first (such as anextruded fiber) and then pyrolyzed to give a silicon nitride-containingfiber. The hydrosilazane polymers can be filled with ceramic typefillers (if desired) and then fired to at least 750° C. to obtainsilicon nitride ceramic materials or silicon nitride ceramicmaterial-containing ceramic articles.

The polymers of this invention can be used in both the filled andunfilled state, depending on the application. Thus, it is contemplatedwithin the scope of this invention to coat substrates with filled andunfilled polymers and heat the substrates to produce siliconnitride-containing ceramic coated articles. Fillers and adjuvants can bemilled on 3 roll mills by simply mixing the hydrosilazane polymers ofthis invention with the fillers and making several passes on the mill.In the alternative, the polymers can be placed in solvents and thefillers and adjuvants can be added thereto and after mixing the solventcan be removed to give the filled polymer. The coating can be carriedout by conventional means. The means used depends on the polymer andsubstrates used and the application one has in mind. Thus, thesematerials can be brushed, rolled, dipped or sprayed. In the filledstate, it is sometimes necessary to trowel the polymer onto thesubstrate.

Whenever the polymers are converted to the ceramic state, it is done bypyrolyzing the polymer to a temperature of at least 750° C. in an inertatmosphere or in a vacuum.

So that those skilled in the art can better appreciate and understandthe invention, the following examples are given. Unless otherwiseindicated, all percentages are by weight.

In the following examples, the analytical methods used were as follows:

Percent Silicon was determined by a fusion technique which consisted ofconverting the silicon material to soluble forms of silicon and thenanalyzing the soluble material quantitatively for total silicon byatomic absorption spectrometry. Solubilization takes place by weighingthe sample into a Parr-type fusion cup (about 0.3 gm), adding 15.0 gmsof sodium peroxide, heating for about 90 sec. and quenching in coldwater. The material is placed in a nickel beaker containing 150-200 ml.of distilled water. Reagent grade acetic acid (55 ml.) is added anddiluted with water to 500 ml. volume.

Percent Chlorine (residual) was determined by sodium peroxidedecomposition and titration with silver nitrate. Fusion of the halideswith sodium peroxide is followed by potentiometric titration withstandard silver nitrate by weighing a sample into a gelation capsule,placing about 1.5 gm. of Na₂ O₂, about 0.7 gm of KNO₃ and about 0.15 gmof sugar into a clean, dry reaction cup and burying the capsule in themixture. The cup is filled with Na₂ O₂ and placed in a reaction vessel.It is heated for 111/2 min. and quenched in cold water. The cup andvessel are washed and the washings are collected. The washings areheated to dissolve any solids. Cold 50% aqueous H₂ SO₄ (15 ml.) is addedand allowed to stand 15-20 sec. This solution is neutralized withadditional H₂ SO₄ and tritrated.

Carbon, hydrogen, and nitrogen were determined on a C, H, N ElementalAnalyzer, model 1106, manufactured by Carlo Erba Strumentazione ofItaly. The sample was combusted at 1030° C. and then passed over achromium oxide bed at 650° C. and a copper bed at 650° C. The N₂, CO₂,and H₂ O produced were then separated and detected using a thermalconductivity detector.

The hydrosilazane polymers were fired to elevated temperature using anAstro Industries Furnace 1000A water cooled graphite heated model1000.3060-FP-12. Samples fired to 1600° C. were heated in a inertatmosphere using the following temperature program: 25° to 380° C. at2.9° C./min.; 380° to 600° C. at 2.6° C./min.; 600° to 850° C. at 5.2°C./min.; 850° to 1600° C. at 31.3° C./min.; hold at 1600° C. for 12minutes; followed by cooling at a rate of about 13° C./min.Hydrosilazane polymers fired at 1300° C. were heated in an inertatmosphere using the following temperature program: rapid heating to740° C.; 740° to 800° C. at 0.83° C./min; 800°-1300° C. at 2.1° C./min;followed by cooling.

EXAMPLE 1

The reaction system consisted of a 2 liter, 3-neck glass flask equippedwith a heating mantle, a temperature controller, a paddle stirrer, adistillation apparatus, and a gas inlet tube. After purging the systemwith argon, 800 g of [(CH₃)₃ Si]₂ NH (5 moles) and 300 g HSiCl₃ (2.2moles) were added to the reaction system at room temperature. Themixture exothermed to about 75° C. The reactants were then heated to230° C. at a rate of about 0.5° C./minute under an argon atmosphere. Thetemperature was held at 230° C. for about 10 minutes. The product wasallowed to cool to about 140° C. under argon at which time the productwas vacuum stripped at 150° C. and 37 mm Hg. After backfilling withargon the hydrosilazane polymer was heated to 180° C., poured into argonblanketed containers, and then cooled overnight under argon. A polymeryield of about 190 g was obtained. The polymer was a clear light yellowsolid which could be shaped with pressure. IR analysis showed thepresence of SiH, Si(CH₃)₃, and SiCl groups. The total chloride contentwas less than 0.08 percent. The silicon content was 48.0 percent. The C,H, N analysis gave C at 22.7 percent, H at 7.8 percent, and N at 21.5percent.

A melt rheometer with a 3/8 inch heat barrel and 20 micron spinneret wasemployed to prepare fibers from this hydrosilazane polymer. The bestfibers were prepared at about 70° C.

A sample of the hydrosilazane polymer was fired to 1600° C. under heliumin the Astro furnace. A dark green ceramic material was obtained with ayield of 53.1 percent. X-ray analysis gave 35 percent α-Si₃ N₄ with noβ-SiC detected. The ceramic product contained 62 percent silicon.

Samples of the hydrosilazane polymer were stored at room temperature inbulk form under argon and then fired in the Astro furnace after varyingstorage times. Physical changes, including solubility in organicsolvents such as toluene, were not observed after storage for theindicated times.

    __________________________________________________________________________    STORAGE                     CERAMIC                                           TIME         FIRING CONDITIONS                                                                            YIELD                                             SAMPLE                                                                              (DAYS) ATMOSPHERE                                                                             TEMP(° C.)                                                                   (%)   APPEARANCE                                  __________________________________________________________________________    A     40     Helium   1600  52.8  green-black                                 B     50     Nitrogen 1600  53.7  green-black                                 C     56     Helium   1600  59.3  black                                       D     64     Helium   1600  55.5  gray-black                                  __________________________________________________________________________

Sample A contained 43 percent α-Si₃ N₄ and 13 percent β-SiC by X-rayanalysis. Sample B contained about 43 percent α-Si₃ N₄ and about 15percent β-SiC.

EXAMPLE 2

Using the same materials and procedures as in Example 1, except asnoted, 400 g (2.5 moles) of [(CH₃)₃ Si]₂ NH and 150 g (1.1 moles) HSiCl₃were reacted. The reaction mixture was heated to 190° C. at a rate of0.5° C./minute and then cooled to room temperature overnight. Thematerial was a clear yellow liquid of moderately high viscosity. Heatingof this material was continued at a rate of 0.5° C./minute up to a finaltemperature of 260° C. The temperature was held at 260° C. for about 5minutes. Still under argon, the reaction mixture was cooled to about100° C. The mixture was now a clear light yellow, extremely viscous,gumlike material. A product was obtained by vacuum stripping at 200° C.and 5 mm mercury pressure. Upon cooling to room temperature under argon,a light yellow solid which cracked under pressure was obtained. Thismaterial was not flowable even at 250° C.

EXAMPLE 3

Several runs were made with the same HSiCl₃ sample used in Example 1except that the HSiCl₃ sample had been opened to the atmosphere severaltimes. Using the same disilazane and procedure as given in Example 1,the reaction did not proceed as expected but rather began to foam andgel as the reaction temperature went above about 215° C. Satisfactorypolymers were not prepared when the reaction mixture foamed and gelledat elevated temperature.

Several attempts were made to overcome this problem by adding the HSiCl₃at dry ice/acetone temperatures and at such a rate to keep the initialtemperature due to the reaction exotherm below about 35° C. When thereaction temperature was raised above about 225° C. foaming, followed bygellation, again occurred.

Finally the HSiCl₃ was purified by simple distillation. The glassdistillation apparatus was dried overnight with a dried argon purge. Themiddle 80 percent of the overhead material was collected and storedunder an argon atmosphere. Gas liquid chromatography analysis indicatedthat the sample was greater than 99.7 percent HSiCl₃.

A hydrosilazane polymer was prepared using this purified HSiCl₃ and thedisilazane employed in Example 1. The apparatus and procedures, exceptas noted, were as described in Example 1. Purified HSiCl₃ (140.5 g, 1.04mole) at dry ice/acetone temperature was added slowly to 375 g (2.3moles) of [(CH₃)₃ Si]₂ NH. The HSiCl₃ addition took place over about 45minutes during which time the reaction temperature rose to about 32° C.The reaction mixture was stirred at room temperature under argonovernight. The temperature was then raised to 245° C. at a rate of 0.5°C./minute. No significant foaming was observed. After the reactionmixture reached 245° C. the mixture was cooled to about 170° C. and thenvacuum stripped at a pressure of about 45 mm mercury. The product wascollected and cooled overnight under argon. The product was a clear,very light yellow solid. Although the material could be shaped somewhatwith pressure there was some tendency to crack.

The polymer was evaluated in a similar spinning apparatus as describedin Example 1 using a 20 micron spinneret. Continuous fibers could beprepared at temperatures from about 83° C. to 92° C. Spinningtemperatures above 92° C. were not evaluated.

A number average molecular weight of about 1700 g/mole for thehydrosilazane polymer was determined by vapor pressure osmometry usingtetrahydrofuran as solvent.

Samples of the hydrosilazane polymer, which had been stored in bulk format room temperature under argon, were fired in the Astro furnace aftervarying storage times. No physical changes, including solubility inorganic solvents such as toluene, were observed after storage for theindicated times.

    __________________________________________________________________________    STORAGE                     CERAMIC                                           TIME         FIRING CONDITIONS                                                                            YIELD                                             SAMPLE                                                                              (DAYS) ATMOSPHERE                                                                             TEMP(° C.)                                                                   (%)   APPEARANCE                                  __________________________________________________________________________    A     17     Helium   1600  55.2  green-black                                 B     37     Helium   1300  59.0  shiny-black                                 C     148    Helium   1600  54.4  green-black                                 __________________________________________________________________________

According to X-ray analysis Sample A contained 63 percent αSi₃ N₄ and 22percent βSiC. Sample C contained 56 percent αSi₃ N₄ and 5 percent αSiC.

EXAMPLE 4

This example demonstrates the preparation of a hydrosilazane polymerfrom [H(CH₃)₂ Si]₂ NH and HSiCl₃. Both the disilazane and chlorosilanewere purified by distillation prior to use. The apparatus and procedureswere essentially as described in Example 1. Purified HSiCl₃ (30.0 g,0.22 moles), at room temperature, was quickly added to [H(CH₃)₂ Si]₂ NH(75.2 g, 0.57 moles). The temperature quickly rose to about 55° C. Thetemperature was increased at a rate of 0.5° C./minute to 235° C. Thereaction product was cooled to about 160° C. and then vacuum stripped at170° C. and 14 mm mercury. A polymer yield of18.3 g was obtained. Theproduct was a viscous, cloudy oil with an estimated viscosity of severalhundred centistokes at room temperature. IR analysis showed the presenceof NH, SiH, Si-CH₃, and SiN groups in the polymer. A dark green ceramicpowder was obtained upon firing this hydrosilazane to 1600° C. in ahelium atmosphere. The ceramic yield was 48.3 percent. X-ray analysis ofthe ceramic gave 51 percent αSi₃ N₄ and 8 percent αSiC. The ceramicpowder contained 62.1 percent Si.

That which is claimed is:
 1. A method of preparing a siliconnitride-containing ceramic material which method consists of heating aR₃ SiNH-containing hydrosilazane polymer in an inert atmosphere or in avacuum to a temperature of at least 750° C. until said R₃SiNH-containing hydrosilazane polymer is converted to a siliconnitride-containing ceramic material, said R₃ SiNH-containinghydrosilazane polymer having been obtained by a process which consistedof contacting and reacting, in an inert, essentially anhydrousatmosphere, trichlorosilane with a disilazane at a temperature in therange of 25° to 300° C. while distilling by-produced volatile products,wherein said disilazane had the general formula

    (R.sub.3 Si).sub.2 NH

where R is selected from the group consisting of vinyl, hydrogen,phenyl, and alkyl radicals containing 1 to 3 carbon atoms.
 2. A methodas defined in claim 1 wherein said trichlorosilane was purified prior tocontacting and reacting with said disilazane at a temperature in therange of 125° to 175° C.
 3. A method as defined in claim 1 wherein saidtrichlorosilane and said disilazane were contacted in such a manner thatthe initial reaction temperature resulting from the initial exotherm wasless than 50° C.
 4. A method as defined in claim 2 wherein saidtrichlorosilane and said disilazane were contacted in such a manner thatthe initial reaction temperature resulting from the initial exotherm wasless than 50° C.
 5. A method as defined in claim 3 wherein the initialreaction temperature resulting from the initial exotherm was less than35° C.
 6. A method as defined in claim 4 wherein the initial reactiontemperature resulting from the initial exotherm was less than 35° C. 7.A method as defined in claim 1 wherein (R₃ Si)₂ NH was [(CH₃)₃ Si]₂ NH.8. A method as defined in claim 1 wherein (R₃ Si)₂ NH was [(CH₃)₂ CH₂═CHSi]₂ NH.
 9. A method as defined in claim 1 wherein (R₃ Si)₂ NH was[CH₃ (C₆ H₅)₂ Si]₂ NH.
 10. A method as defined in claim 1 wherein (R₃Si)₂ NH was [C₆ H₅ (CH₃)₂ Si]₂ NH.
 11. A method as defined in claim 1wherein (R₃ Si)₂ NH was [H(CH₃)₂ Si]₂ NH.
 12. A method as defined inclaim 2 wherein (R₃ Si)₂ NH was [(CH₃)₃ Si]₂ NH.
 13. A method as definedin claim 2 wherein (R₃ Si)₂ NH was [(CH₃)₂ CH₂ ═CHSi]₂ NH.
 14. A methodas defined in claim 2 wherein (R₃ Si)₂ NH was [CH₃ (C₆ H₅)₂ Si]₂ NH. 15.A method as defined in claim 2 wherein (R₃ Si)₂ NH was [C₆ H₅ (CH₃)₂Si]₂ NH.
 16. A method as defined in claim 2 wherein (R₃ Si)₂ NH was[H(CH₃)₂ Si]₂ NH.
 17. A method as defined in claim 4 wherein (R₃ Si)₂ NHwas [(CH₃)₃ Si]₂ NH.
 18. A method as defined in claim 4 wherein (R₃ Si)₂NH was [(CH₃)₂ CH₂ ═CHSi]₂ NH.
 19. A method as defined in claim 4wherein (R₃ Si)₂ NH was [CH₃ (C₆ H₅)₂ Si]₂ NH.
 20. A method as definedin claim 4 wherein (R₃ Si)₂ NH was [C₆ H₅ (CH₃)₂ Si]₂ NH.
 21. A methodas defined in claim 4 wherein (R₃ Si)₂ NH was [H(CH₃)₂ Si]₂ NH.
 22. Asilicon nitride-containing ceramic material as prepared by the method ofclaim
 1. 23. A silicon nitride-containing ceramic material as preparedby the method of claim
 2. 24. A silicon nitride-containing ceramicmaterial as prepared by the method of claim 4.